Sun seeker



Feb. 19, 1963 P. w. CHASE ETAL SUN SEEKER 4 Sheets-Sheet 2 Filed Oct. 13, 1960 Feb. 19, 1963 P. w. CHASE ETAL SUN SEEKER 4 Sheets-Sheet 3 Filed 00t- 13. 1960 i H, ,Imm &\ IN2: Z I :wm m @Lm @d mw wm j @n h r@ uw www Feb. 19, 1963 P. w. CHASE ETAL 3,078,372

SUN SEEKER Filed Oct. 13, 1960 4 Sheets-Sheet 4 United States Patent O 3,078,372 SUN SEEKER Paul W. Chase, Mount Iron, and Robert L. Howard aud Jantes W. Stoddart, White Bear Lake, Minn., assignors, by mestre assignments, to t' e United' States of America as represented by the Secretary of the Navy Filed Oct. 13, 1960, Ser. No. 62,513

8 Claims. (Ci. Z50-203) This invention relates to apparatus for aiming at the sun or other relatively moving bright source ot light, heat, or other radiant energy.

An object of the invention is to provide such an apparatus with protection against simultaneous saturation of its sensors by the sun or other strong radiant energy source.

A further object is to provide a device of improved angular sensitivity for orienting a scientific instrument or device relative to a bright source of radiant energy.

Another object is to provide a device of this type which is small, simple, rugged, efcient, sensitive, inexpensive, and light-weight to be carried by a high altitude balloon.

AFurther objects and advantages of the invention will appear as the description proceeds.

The invention will be better understood on reference to the following description and the accompanying drawing, wherein:

FIG. l is a schematic view of a balloon in ight carrying a sun seeker constructed and arranged in accordance with the invention.

FIG. 2 is a top plan view of the seeker.

FIG. 3 is a right side elevational View of the seeker.

FIG. 4 is a sectional view taken at 4 4 in FIG. 3.

FIG. 5 is a front elevational view of the seeker.

FIG. 6 is a block diagram of a circuit which may be employed in the seeker.

FIG. 7 is a block diagram of a modified circuit.

Referring now more particularly to the drawing, disclosing an illustrative embodiment of the invention, there is shown at 10 (FIG. l) a high altitude balloon preferably formed of polyethylene or Mylar or other suitable plastic lm to float at a desired ceiling altitude. The balloon load line 12 passes through and supports an electrically-fired or other suitable line cutter 13 and suspends a parachute 14 from which hangs a gondola 16 carrying a telescope 18 which may be equipped with a photomultiplier and whose objective lens 20 is shown with its axis vertical. Mounted on and over the gondola 16 is an inverted U-bracket 22 whose base 23 has a central split socket 24 (FIGS. 4 and 5) clamped alat 26 about the hub 28 of a gear 30 coaxial with the cns 20, the axis being indicated at 32. The gear 30 is journaled about a vertical axle 34 xed as by nuts 3640 the base 38 of a U-shaped chassis 49 forming part of a sun seeker 41. A planetary pinion 42 meshing with the gear 30 is driven at low saeeds by a reversible motor 44 mounted as at 46 on the chassis base 3S.

A mirror 59, whose reflecting surface 52 is inclined at a suitable angle to the vertical and intersects the axis 32, is arranged between the lens 20 and the axle 34 and is 'secured as at 54 to a bracket S6 having a sleeve 58 secured as at 60 to the axle. When the motor 44 runs, the pinion 42 orbits about the gear 30 and thus rotates the mirror 5G and the chassis 40 about the axis 32.

The means for driving the motor 44 will now be dcscribed.

Secured as at 64 to the outer face 66 of the chassis arm 68 is a wall 7G having a hole 72 in line with a hole 74 in said arm. At the inner face of the chassis arm 68 is secured radiant-energy-sensing means which, in the case of a bright light source, for example the sun, comprises a photo-transistor unit 76 including a pair of senslll "ice

ing elements in the holes 72 and 74, the sensing elements having at their front ends respectively left and right eyes or sensors78 and 8G at the front face 82 of the wall and facing forward, i.e., away from the chassis 40. Vanes 84 and 86 adjoin and extend forward from the wall 70 from levels adjacent and respectively above and below the tops and bottoms of the sensors 78 and 80. An opaquegscreenogseptumh whose plane contains the axis 32 and is normal to and intersects the mirror surface 52, wall 70 and Vanes 84 and 86, adjoins and extends forward from the wall and preferably symmetrically partitions oil and occludcs the sensors 78 and 80 from each other, the vanes and septum being slotted to enable the septum to accommodate the vanes. The Vanes 84 and 86 are preferably welded as at 90 at their junctures with the wall 70 and septum 88. The vane 86 is an opaque screen or shield inclined downward from the wall 70 at an angle such that the sensors 78 and 80 can substantially just see the horizon when the balloon is at ceiling altitude, so that the sensors can be excited by radiation from approaching sunrise and after sunset as well as from the sun when it is above the horizon. The welding 90 joining the vane 86 to the septum 88 is preferably at both faces of the septum, and lightsealing putty 92 is preferably applied at the bottom trihedral corners, where the welding may be incomplete, to prevent ground glow from access to the sensors 78 and 80 through the junctures ot the vane with the wall 70 and septum. The Vanes 84 and 86 serve as reinforcements for the septum 88. If the septum 88 is otherwise suitably reinforced, the vane 84 may be dispensed with. The vane 84 may be opaque. inasmuch as different bal loons 10 having ditlerent ceiling altitudes may be used, and on dil-ferent days the trajectories of the sun vary, the vane 84, if used, is set to enable the sensors 78 and 80 to see the sun for the lowest ceiling altitude at which observations are to be made and the highest sun trajectory which is to be observed, and the vane S6 is set to see the horizon as noted above.

An arcuate masking band at the forepart of the septum 88 is welded or otherwise suitably connected at its respective ends 102 to the Vanes 84 and 86. The distance between the mutually remote ends 104 and 106 of the respective sensors 78 and 80 slightly exceeds the width of the shadow cast by the band 100 when the plane of the septum 8S bisccts the sun or otherl bright light source. so that the band then masks or shades only the mutually adjacent major portions of the sensors, leaving identical relatively small outer circular segment areas of the sensors to receive light from the sun. The sun subtends an angle of about V2" at the earth. Using sensors 21/1 mm. in diameter, with their centers 9 mm. apart, and a band 100 having a width of l0 mm. and located 4% from the eyes, then, when the sensors are equally masked by the band, each exposed sensor segment will have a radial extent, ie., rise, of 3,3 mm.

The entire bottom surface of the shield 86, both sides of the septum 88 below the shield, the exposed surfaces of the putty 92, the entire front face 82 of the wall 70 below the shield, and all of the other surfaces (other than the mirror surface S2) from which light might otherwise be reflected to the lens 20, are painted a matte black or otherwise suitably coated to protect the lens from reflected sunlight other than from the mirror surface.

The sensors 78 and 80 are of course identical and form parts of a push-push bridge 118 including a battery 120, identical xed resistors 122 and 124, and a balancing potentiometer 126. The bridge 118 may be connected to the input 128 of a high gain transistor D.C. amplifier 130 connected through a transistor power amplir er 132 to the motor 44, all as shown in the block diagram of FIG. 6. In calibration, the potentiometer 126 is adjusted to and fixed in a condition such that, when the sensors 78 and 80 are equally excited, no signal voltage appears at the input 128, and accordingly the bridge 118 is balanced, so that the motor 44 does not run. If desired, the circuit may have a dither voltage impressed upon it (FIG. 7). This sawtooth voltage, supplied by the generator 134 and applied to the input 128, tends to give velocity modulation to the servo motor 44, and, by driving the signal back and forth through any potential dead spot, eliminates the dead spot.

When the sun is forward of the wall 70 and predominantly or entirely at a side of the plane of the septum 88, the sensor at that side receives more sunlight and accordingly is more excited than the other sensor, so that a voltage, negative or positive, depending on which side is involved, appears at the input 128. This voltage is amplied and, when the amplified voltage applied to the motor 44 exceeds the minimum necessary to overcome friction and inertia, the motor runs in one direction 136 or the other 138, according as the voltage is negative or positive, the direction in each case being such as to turn the chassis 40 and chassis-supported structure, including the mirror 50, in that direction, 140 or 142, aS the case may be, which will bring the plane of the septum 88 closer to the center of the sun and thus tend to equalize the intensities of sunlight exciting the sensors 78 and 80. The amount of the voltage and hence the speed of the cmotor 44 being dependent on the difference in such intensities, it follows that, when only one sensor is excited lby the energy source, the motor speed is relatively high. When the other sensor begins to become excited, the voltage begins to lessen and hence the motor begins to decelerate, so that, when both sensors become nearly equally excited, the motor stops, with the mirror surface 52 in a desired position, relative to the sun, to reiiect to the lens 20 sky light azimuthally 90 from the sun. Of course, the mirror 50 could instead be so mounted on the axle 34 that the surface 52 will reflect radiant energy from the sun or any sky light whose position is determined by the sun.

If no masking band or the like were used, and the sun were directly ahead of the septum 88, then, on bisection of the sun by the plane of the septum, the entire sensors 78 and 80 would simultaneously see and thus be saturated by the sun, with resultant loss in sensitivity of the bridge 118.

If the masking band were of such width as to be capable of simultaneously shading both sensors 78 and 80 completely from the sun, and assuming this condition existed, so that the edges of the shadow cast by the band were at the outer ends 104 and 106 of the respective sensors, then a small shift of the sun from the plane of the septum 88 would cause the shadow to uncover the outer end porytion (a circular segment) of one sensor say the sensor mum before the motor will run, as noted above, and the sensor area progressively uncovered is abou-t 1.7 mm. circular segment rise per degree of shift of the sun for the dimensions given above, the suns shift would have to be possibly as-much as, say, 1/z before the voltage would be great enough to start the motor. Then, on return of the shadow to a position in which it still does not completely occult the sensor 78, but where the resulting voltage is below the minimum, the motor will stop, with the sensors off target by nearly 1/2. Since the same would be true in the opposite sense if the sun were at the other side of the plane of the septum 88, the total error i.e., angle of insensitivity, would then be about 1 of shift of the sun. That is, near target, the device would then be insensitive to about 1 shift of the sun from one side of the septum 88 to the other.

With the band 100 as shown and described so that it cannot completely occult both sensors simultaneously, and assuming the sun is ahead, and bisected by the plane,

of the septum 88, then the edges of the shadow cast by the band reveal to the sun identical mutually remote circular segments of the sensors 78 and 80. As noted above, for the example given, each such unshadowed segment would then have a rise of 3A mm. Now, initial azimuthal shift of the sun to one side of the plane of the septum 88 will uncover a relatively large additional area of one sensor (compared to that uncovered for a like shift of the sun if the shadow had just completely occulted both eyes before the shift), and will at the same time occult a somewhat smaller, but nevertheless substantial, additional area of the other sensor, producing the minimum operative voltage with a substantially smaller azimuthal shift of the sun, so that the device is much more sensitive to azimuthal shift of the sun if the band cannot completely occult both sensors simultaneously than would be the case if the band could so occult both sensors. With the parts dimensioned as above, the total azimuthal angle of insensitivity has been found not to exceed about l/2 of shift of the sun from one side to the other of the septum 88.

IIt is apparent that the sensors 78 and 80 will follow azimuthally and center on or point to the brightest or substantially the brightest portion of the sky just before sunrise and just after sunset, unhindered by the band i100, due to the relatively wide and diffuse character of such light. For this reason, and because the brightness :before sunrise and after sunset is so much weaker than that of direct sunlight, simultaneous substantially full exposure of the sensors to the before-sunrise light and after-sunset light will not saturate the sensors 78 and 80.

vIn the case where the observations are to take place at the ceiling altitude at which the balloon is designed to float, say 100,000 ft. more or less, the time required for the balloon to reach that altitude may be up to about two hours, more or less, and will have been predetermined in accordance with well known high altitude balloon flight design practice. In order to conserve the battery 120, a switch, controlled as by a timer or aneroid lharornetric pressure device by the balloon 10, or controlled by radio command from the ground, may be employed to close the circuit when ceiling altitude is reached. However, in the interest of low cost, the switch is preferably omitted, the circuit being closed when the balloon 10 is about to be launched.

The seeking apparatus initially may be so oriented that the sun is behind the eyes 78 and 80. This presents no problem, however. If the sun happens to be centered belhind the senors 78 and 80, this condition will exist only momentarily, since the sun is moving. Once the sun shifts to a position in which, although behind the sensors 78 and :80, is is all or predominantly at one side, say the left, of the plane of the septum 88, the sky glow visible to the sensor 78 will be brighter than the sky glow visible to the sensor 80, with the result that a voltage will be produced to turn the chassis 40 in the direction tending to face the sensor 78 toward the sun, and this running of the motor will continue with increasing speed until the shadow cast by the band 100 begins to occult the sensor 78. If instead the sun happened to be all or predominantly at the right tof the plane of the septum, the motor 44 would turn in the opposite direction to bring about corespoudingly the same desired result.

The various elements of the circuitry may be carried by or housed in the chassis 40, which, together with the wall `70, the vanes 84 and 86, and the septum 88, is preferably of light weight sheet metal such as aluminum, and the entire apparatus is compact and light in weight, which of course is especially desirable for balloon ight.

Obviously many modifications and variations of the invention are possible in the light of the above teachings. It is therefore to be understood that within the scope of the appended claims the invention may be practiced otherwise `than as specifically described.

We claim:

1. In combination with a high altitude plastic lm ba1- loon having a predetermined ceiling altitude, and a gondola suspended from the balloon, observation means including a telescope carried by the gondola with the axis of its objective lens vertical, a gear coaxial with the lens and fixed to the gondola, a chassis above the gondola, an axle fixed to the chassis and journaled in the gear, a reversible motor mounted on the chassis, a pinion driven by the motor and meshing the gear, left and right forwardly facing photo sensors carried by the chassis, means responsive to unequal excitation of the sensors by the sun for driving the motor in that direction, depending on which sensor is the more excited, which tends to equalize the excitation, a mirror fixed to the axle and intersecting said axis and inclined to the vertical in a position to receive sky light moving with the sun and reect it to the lens when the sensors are substantially equally excited by the sun, a vertical opaque septum whose plane is normal to that of the mirror and contains said axis, the septum partitioning the sensors from each other and extending forward relative to the sensors, an arcuate mask spaced from the sensors and secured to a forepart of the septum and extending across the septum from a level below that of the sensors to a level above that of the sensors, the sensors being located substantially at the axis of the mask, the elevation angle subtended by the mask being at least coincident with the angle of elevation of the sun from the horizon at sunrise to the top of the suns trajectory when the balloon is at ceiling altitude, the width of the shadow cast by the mask on the sensors being substantially greater than the distance between the centers of the sensors and less than the distance between the mutually remote ends of the sensors, and means occluding the sensors from ground glow when the balloon is at ceiling altitude.

2. In a sun seeker assembly mounted to rotate about a vertical axis and comprising left and right sunlight sensors and an opaque septum between and extending forward from the sensors, an opaque arcuate band of uniform width spaced forward and upward from the sensors, the line extending from center to center of the sensors being horizontal and substantially at the axis of the band, the band and said line being bisected by the same vertical plane, the distance between the mutually remote ends of the sensors being at least as great as the width of the shadow cast on the sensors by the band when said plane bisects the sun, and means responsive to a predetermined minimum difference in excitation of the sensors by radiant energy from the sun to rotate the assembly in that direction, depending on which sensor is the more excited, which tends to equalize the excitation.

3. The structure of claim 2, characterized in that said width is less than the distance between the mutually remote ends of the sensors.

4. The structure of claim 2, characterized in that said width is at least substantially equal to the length of said line.

5. In a sun seeker assembly mounted to rotate about a vertical axis and comprising left and right sunlight sensors and an opaque septum between and extending forward from the sensors, an opaque band of uniform width spaced forward from the sensors, the band and the line from center to center of the sensors being bisected by the same vertical plane, the distance between the mutually remote ends of the sensors being at least as great as the width of the shadow cast on the sensors by the band when said plane bisects the sun, and means responsive to a predetermined minimum ditierence in excitation of the sensors by radiant energy from the sun to rotation the assembly in that direction which tends to equalize the excitation.

6. The structure of claim 5, characterized in that said width is less than the distance between the mutually remote ends of the sensors.

7. The structure of claim 5, characterized in that said width is at least substantially equal to the length of said line.

8. In a sun seeker assembly mounted to rotate about a vertical axis and comprising left and right sensors, an opaque non-reective septum between and extending forward from the sensors, an opaque band of uniform width disposed at the forward part of the septum, the band and the line extending from center to center of the sensors being bisected by the same vertical plane, the distance between the mutually remote ends of the sensors being at least as great as the width of the shadow cast on the sensors by the band when said plane bisects the sun, and means responsive to a predetermined minimum dierence in excitation of the sensors by radiant energy from the sun to rotate the assembly in that direction which tends to equalize the excitation.

References Cited in the file of this patent UNITED STATES PATENTS 2,155,402 Clark Apr. 25, 1939 2,277,692 Dunmore Mar. 3l, 1942 2,604,601 Menzel July 22, 1952 2,976,758 Parker Mar. 28, 1961 2,999,163 Beese Sept. 5, 1961 3,020,406 Whitney Feb. 6, 1962 

2. IN A SUN SEEKER ASSEMBLY MOUNTED TO ROTATE ABOUT A VERTICAL AXIS AND COMPRISING LEFT AND RIGHT SUNLIGHT SENSORS AND AN OPAQUE SEPTUM BETWEEN AND EXTENDING FORWARD FROM THE SENSORS, AN OPAQUE ARCUATE BAND OF UNIFORM WIDTH SPACED FORWARD AND UPWARD FROM THE SENSORS, THE LINE EXTENDING FROM CENTER TO CENTER OF THE SENSORS BEING HORIZONTAL AND SUBSTANTIALLY AT THE AXIS OF THE BAND, THE BAND AND SAID LINE BEING BISECTED BY THE SAME VERTICAL PLANE, THE DISTANCE BETWEEN THE MUTUALLY REMOTE ENDS OF THE SENSORS BEING AT LEAST AS GREAT AS THE WIDTH OF THE SHADOW CAST ON THE SENSORS BY THE BAND WHEN SAID PLANE BISECTS THE SUN, AND MEANS RESPONSIVE TO A PREDETERMINED MINIMUM DIFFERENCE IN EXCITATION OF THE SENSORS BY RADIANT ENERGY FROM THE SUN TO ROTATE THE ASSEMBLY IN THAT DIREC- 